Meowy Catkin
Meow!
I also agree he's off.
My junior car has been off behind for some time: just a bit of a John Wayne walk intitally. Wouldn't move at the vets, but had a "pain" reaction to having two thumbs very firmly and suddenly pressed into her hips (I am not convinced it wasn't just surprise). X rays showed nothing. She can still climb fences but in the last few weeks is starting to get a bit clumsy in things like getting off my knee, but still nothing you can really capture on video or that will display at a vet.
I will be really interested to hear if you pinpoint anything with yours!
The fact that cats hide their issues so well at the vets, even if it's by refusing to move, makes it so hard for the vet to see the true picture.
I hope your cat is sound again soon.